The present invention relates to a power supply arrangement for an audio system such as may be employed in a television receiver.
Television receivers have loudspeakers included within the cabinet of the television receiver which are permanently connected to the signal providing power output stages. Some television receivers, especially those with stereophonic sound and other multiple channel sound processing sections, have provisions for connecting additional loudspeakers to the receiver. One multiple channel sound processing system is known as "PROLOGIC".TM. sound system. The "PROLOGIC".TM. system has four sound channels (left, center, right, and surround) instead of just the normal left and right stereophonic sound channels.
The additional channels can cause the doubling of the total power drawn from the power supply which provides power to the audio system. For reasons of economy, it is often desirable not to have to double the power providing capacity of the power supply to accommodate two extra loudspeakers which may, or may not, be connected to the television receiver. An increased the power supply capacity can require substantially larger components, having additional cost and weight, require additional space in the television receiver, and increase the heat generated within the receiver chassis. Additionally, if the power is drawn from the horizontal flyback circuit, there can be a problem with audio modulation of the video display.
Accordingly, it is desirable to maintain essentially the same audio power output from the receiver and the corresponding power supply providing power to the audio circuits whether or not the additional speaker connections to the television receiver are utilized.
In the CTC-130 color television chassis of the RCA Corporation of Indianapolis, Ind., USA, a power supply protection circuit is used for protecting the individual audio power amplifiers when an improper load, i.e., a short circuit or the like, is connected to the output. Specifically, in the CTC-130 chassis, a resistor is connected in series between the power supply and the power amplifiers, and a sensing circuit is used to sense the current drawn through the resistor. When the current drawn from the power supply exceeds a predetermined value, the sensing circuit reduces the control voltage to the electronic volume control terminals of the respective power amplifiers. As a result, the current drawn from the power supply is reduced and damage to the power output stages is prevented.